This invention relates to a method of inducing a reversible resistance change by applying electric pulses, in which the character of the resistance change, i.e., increase or decrease, is determined by the pulse duration time, and fabrication of a memory device incorporating the method of the invention.
Perovskite metal oxide thin films, such as Pr0.3Ca0.7MnO3 (PCMO), exhibit reversible resistance change when an electric pulse is applied. A PCMO thin film has been grown on both epitaxial YBa2Cu3O7 (YBCO) and partial epitaxial Pt substrates via pulsed laser abrasion (PLA) technique, Liu et al., Electric-pulse-induced reversible resistance change effect in magnetoresistive films, Applied Physics Letters, 76, 2749, 2000; and Liu et al., U.S. Pat. No. 6,204,139, granted Mar. 20, 2001, for Method of switching the properties of perovskite materials used in thin film resistors. X-Ray diffraction (XRD) polar figures confirm the epitaxial properties of PCMO thin films.
U.S. Pat. No. 6,204,139 describes the resistance change which occurred when electric pulses are applied at room temperature to PCMO thin films. The PCMO thin films were deposited on both epitaxial YBa2Cu3O7 (YBCO) and partial epitaxial Pt substrates by pulsed laser deposition (PLD). The polarity of the electric pulse determines the character of the resistance change, i.e., increase or decrease.
An electrically programmable resistance, non-volatile memory device, operable at room temperature, was made of PCMO epitaxially grown on YBCO on LaAlO3, as published by Liu et al. This type of memory may be reversibly programmed by a reversed short electrical pulse. The memory cell is able to produce either single bit or multi-bit information. However, the PCMO must be in crystalline form, which requires that the PCMO must be grown on a specific bottom electrode, such as YBCO, which is not compatible to the stare-of-the-art silicon integrated circuit technology. The growth, or crystallization, temperature is relatively high, e.g.,  greater than 700xc2x0 C., which makes integration of the device into state-of-the-art integrated circuit very complex. In addition it is not possible to cover the fill circuit area with a single grain of PCMO. As the properties of a memory cell which is fabricated on a single grain PCMO crystal and the properties of a memory cell which is fabricated on a multi-grain PCMO crystal, which covers the grain boundary area, are not the same, circuit yield and memory performance problems will occur.
A method of fabricating a variable resistance device, wherein the resistance is changed by passing a voltage of various pulse lengths through the device, includes preparing a silicon substrate; forming a silicon oxide layer on the substrate; depositing a first metal layer on the silicon oxide, wherein the metal of the first metal layer is taken from the group of metals consisting of platinum and iridium; depositing a perovskite metal oxide thin film on the first metal layer; depositing a second metal layer on the perovskite metal oxide, wherein the metal of the second metal layer is taken from the group of metals consisting of platinum and iridium; annealing the structure at a temperature of between about 400xc2x0 C. to 550xc2x0 C. for between about ten minutes and three hours; and completing the variable resistance device.
A variable resistance R-RAM device includes a silicon substrate having a silicon oxide layer thereon; a first metal layer formed on the silicon oxide layer, wherein the metal of the first metal layer is taken from the group of metals consisting of platinum and iridium; a perovskite metal oxide thin film layer formed on the first metal layer; a second metal layer formed on the perovskite metal oxide, wherein the metal of the second metal layer is taken from the group of metals consisting of platinum and iridium; and metallizing elements to provide a complete device.
It is an object of the invention to provide a method of making a resistance change in an R-RAM device with a single polarity pulse.
Another object of the invention to provide a method of making a resistance change in an R-RAM device by varying the length of resistance-change-producing pulse.
A further object of the invention is to provide an R-RAM device which includes fabricating a PCMO layer on a metal layer.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.